Piezoelectric ceramic composition for surface acoustic wave device and surface a coustic wave device

ABSTRACT

A piezoelectric ceramic composition for a surface acoustic wave device which can improve the electromechanical coupling coefficient is provided. The piezoelectric ceramic composition for a surface acoustic wave device is represented by the formula Pb a Zr x Ti y (Ni m Mn n Nb 2/3 ) z O 3 , wherein x+y+z=1, 0.93≦a≦1.02, 0.32≦x≦0.50, 0.41≦y≦0.54, 0.03≦z≦0.21 and 0.24≦m+n≦0.67.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a piezoelectric ceramiccomposition used for a surface acoustic wave device. In particular, thepresent invention relates to a piezoelectric ceramic composition for asurface acoustic wave device which can improve the impedance ratio andcoupling coefficient and such a surface acoustic wave device.

[0003] 2. Description of the Related Art

[0004] In recent years, accompanying the progress of mobilecommunication equipment using high frequencies, components used therein,for example, resonators and filters, have also been required for use inhigher frequencies and miniaturization. As the resonators and thefilters, surface acoustic wave devices have been used because ofadvantages in acceleration of use in higher frequencies andminiaturization.

[0005] In a surface acoustic wave device, an interdigital transducer(IDT) composed of at least one pair of interdigital electrodes isconfigured on a piezoelectric substrate, and excitation and reception ofthe surface acoustic wave are performed by the IDT. As a piezoelectricsubstrate material of the surface acoustic wave device, a piezoelectricsingle crystal of, for example, LiTaO₃ and LiNbO₃, or a piezoelectricceramic primarily composed of PbTiO₃, Pb(Ti,Zr)O₃, etc., are used. Alaminate in which piezoelectric thin films, such as ZnO thin films, arelaminated on an insulation substrate or a piezoelectric substrate isalso used as the piezoelectric substrate of the surface acoustic wavedevice.

[0006] When comparisons are made between the piezoelectric singlecrystal and the piezoelectric ceramic, the speed of sound is lower inthe piezoelectric ceramic. Therefore, a piezoelectric substrate made ofpiezoelectric ceramic is preferable in order to miniaturize the surfaceacoustic wave device.

[0007] Coupling coefficients required of piezoelectric substratematerials are different depending on the intended purposes, althoughregarding the piezoelectric single crystal, the coupling coefficient isuniquely defined based on the kind and the cut angle. That is, for asurface acoustic wave device using the piezoelectric single crystal, thepiezoelectric characteristics and temperature characteristics areuniquely defined based on the kind of the single crystal and the cutangle, so that flexibility in design of devices is reduced.

[0008] On the other hand, piezoelectric ceramics, such asPb(Ti,Zr)O₃-based ceramics, have piezoelectric characteristics which canbe varied over a wide range by controlling the composition.

[0009] However, when the piezoelectric ceramics were used as thepiezoelectric substrates of the surface acoustic wave devices in highfrequency regions exceeding 10 MHZ, there was a problem in thatimpedance ratios, that is, the ratios of the impedance at ananti-resonant frequency of Fa to the impedance at a resonant frequencyof Fr, are small.

SUMMARY OF THE INVENTION

[0010] Accordingly, it is an object of the present invention to providea piezoelectric ceramic composition for a surface acoustic wave devicewhich can achieve a high impedance ratio even in high frequency regions.

[0011] The piezoelectric ceramic composition for a surface acoustic wavedevice is represented by a formulaPb_(a)Zr_(x)Ti_(y)(Ni_(m)Mn_(n)Nb_(2/3))_(z)O₃, where:

[0012] x+y+z=1;

[0013] 0.93≦a≦1.02;

[0014] 0.32≦x≦0.50;

[0015] 0.41≦y≦0.54;

[0016] 0.03≦z≦0.21; and

[0017] 0.24≦m+n≦0.67.

[0018] Preferably, m and n fall within the ranges of:

[0019] 0.46≦m+n≦0.67;

[0020] 0.01≦m≦0.66; and

[0021] 0.01≦n≦0.66.

[0022] In the piezoelectric ceramic composition for a surface acousticwave device, at least one element selected from the group consisting ofBa, Ca, and Sr may be substituted for a part of said Pb.

[0023] By sintering the piezoelectric ceramic composition, apiezoelectric ceramic suitable for a piezoelectric substrate of asurface acoustic wave device is obtained. The surface acoustic wavedevice preferably utilizes a SH type surface acoustic wave. In the case,it is preferable that a grain diameter is about 3 μm or less and thesizes of pores and defects in the piezoelectric ceramic are about 3 μmor less. Further, it is preferable that the absolute value of a changerate of resonant frequency with respect to temperature is about 100ppm/° C. or less.

[0024] By using the piezoelectric ceramic composition for a surfaceacoustic wave device according to the present invention, excellentimpedance ratios can be achieved, higher frequencies can be used and thepiezoelectric characteristics can be controlled over a wide range.

[0025] Therefore, a surface acoustic wave device which meets userequirements in higher frequencies and miniaturization can be providedwith ease according to the present invention.

[0026] When m+n is 0.46 or more, but 0.67 or less, m is 0.01 or more but0.66 or less, and n is 0.01 or more but 0.66 or less, a largeelectromechanical coupling coefficient can be achieved.

[0027] Furthermore, when the crystalline particle diameter is about 3 μmor less, and when sizes of the pores and defects in the sinteredmaterial are about 3 μm or less, the impedance ratio can be furtherimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a graph showing changes of the electromechanicalcoupling coefficient kBGS with changes of z; and

[0029]FIG. 2 is a perspective view of an end face reflection typesurface acoustic wave device prepared according to an embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The present invention will be explained below in further detailusing specified examples according to the present invention.

[0031] A piezoelectric ceramic composition for a surface acoustic wavedevice, of the present invention is represented by a formulaPb_(a)Zr_(x)Ti_(y)(Ni_(m)Mn_(n)Nb_(2/3))_(z)O₃, wherein x+y+z=1,0.93≦a≦1.02, 0.32≦x≦0.50, 0.41≦y≦0.54, 0.03≦z≦0.21, and 0.24≦m+n≦0.67.

[0032] The inventors of the present invention have discovered that apiezoelectric ceramic composition composed of at least Pb, Ni, Mn, Nb,Ti, Zr, and O and satisfying the aforementioned formula can improve theaforementioned impedance ratio could be effectively improved in asurface acoustic wave device using the aforementioned piezoelectricceramic composition as a piezoelectric substrate.

[0033] The piezoelectric ceramic composition according to the presentinvention is composed of oxides or carbonates of the elements, asprimary materials, indicated by the aforementioned formula, althoughthat may be composed of metals, other compounds or complex oxidesthereof as materials. Each material may contain impurities, althoughthese have little influence as long as the purity is equivalent to ormore than that of first class grade chemicals. Furthermore, Al₂O₃ andSiO₂ may be admixed therewith during manufacture, and degradation ofpiezoelectric characteristics does not occur by a great degree as longas the concentrations of these impurities are and 1,000 ppm or less.

[0034] In the present invention, when a is less than 0.93 or exceeds1.02, sinterability is degraded so that a sintered material havingsufficient strength cannot be produced due to inferior sinterability.

[0035] When x is less than 0.32 or exceeds 0.50, the impedance ratio andthe electromechanical coupling coefficient are reduced. Likewise, when yis less than 0.41, although the impedance ratio is high, the heatresistance is remarkably degraded. When y exceeds 0.54, theelectromechanical coupling coefficient and the impedance ratio arereduced. Likewise, when z is less than 0.03, or exceeds 0.21, theimpedance ratio and the electromechanical coupling coefficient arereduced.

[0036] In addition, when m+n is 0.24 or less or exceeds 0.67, thesinterability is inferior, and many different phases are present, sothat desired sintered material may not be produced.

[0037] In particular, when m+n is 0.46 or more but 0.67 or less, m is0.01 to 0.66, and n is 0.01 to 0.66, the electromechanical couplingcoefficient can be effectively improved, so that this case ispreferable.

[0038] The piezoelectric ceramic obtained by sintering the piezoelectricceramic composition comprises as a primary component an oxide having aperovskite structure. At least one element selected from the groupconsisting of Ba, Ca and Sr may substitute for Pb constituting A site ofthe perovskite structure, and in such a case, degradation of thepiezoelectric characteristics is not likely to occur. Herein, the rateof substitution of Pb element by Sr, Ba or Ca in the piezoelectricceramic composition is preferably specified to be within the range ofabout 10% by mol or less of Pb.

[0039] Preferably, in the piezoelectric ceramic obtained by sinteringthe piezoelectric ceramic composition, a grain size is specified to beabout 3 μm or less.

[0040] Furthermore, the sizes of pores and defects formed in thepiezoelectric ceramic are preferably specified to be about 3 μm or less.

[0041] In a specified piezoelectric ceramic according to of the presentinvention, the absolute value of a change rate of resonant frequencywith respect to temperature is preferably specified to be about 100ppm/° C. or less.

[0042] The piezoelectric ceramic according to the present invention issuitably used for a surface acoustic wave device using a SH type surfaceacoustic wave. When the SH type surface wave is used, the surfaceacoustic wave device can be further miniaturized compared to a surfaceacoustic wave device using a Rayleigh wave.

[0043] Hereinafter preferred embodiments of the present invention willbe described in more detail.

[0044] As materials, powders of Pb₃O₄, NiO, MnCO₃, Nb₂O₃, TiO₂ and ZrO₂was prepared. These powders were weighed in order to have each ofcompositions as shown in the following Table 1 to Table 5, and afteraddition of water, wet mixing was performed with a ball mill so as toproduce slurry.

[0045] The resulting slurry was dehydrated, and the resulting mixedpowder was dried with an oven and was subjected to particle sizing,thereby obtaining a piezoelectric ceramic composition.

[0046] Subsequently, sized mixed powder was put in a box made ofalumina, and was calcined at a temperature of 800° C. to 1,000° C. so asto produce a calcined material.

[0047] A binder and a dispersing agent were added to the aforementionedcalcined material, and these were wet-mixed with a ball mill so as toproduce a second slurry. The second slurry was poured into a mold havingthe plan shape of a square, and cast molding was performed. Theresulting square plate-like molding was degreased at 300° C. to 600° C.,and thereafter, was baked at 1,000° C. to 1,300° C. in an atmosphere ofoxygen so as to produce a sintered piezoelectric ceramic.

[0048] The surface of the resulting sintered piezoelectric ceramic wasfinished by lapping so as to produce a piezoelectric substrate of 5 cmby 5 cm having a thickness of 0.4 mm to 0.8 mm.

[0049] Polarization electrodes were formed on the piezoelectricsubstrate produced as described above, and polarization was performed at100° C. in oil with field intensity of 3 kV/mm. Thereafter, aging wasperformed at a temperature of 200° C. for 1 hour.

[0050] A plurality of IDTs were formed on the aged piezoelectricsubstrate by photolithography, and each of surface acoustic wave deviceswas cut from the resulting piezoelectric substrate. The surface acousticwave device produced as described above is shown in FIG. 2.

[0051] In the surface acoustic wave device 1, an interdigital transducer(IDTs) 3 is formed on a piezoelectric substrate 2 made of theaforementioned piezoelectric ceramic composition. The outermostelectrode fingers of IDTs 3 are flush with edges made by end faces 2 aand 2 b and the top face of the piezoelectric substrate 2. The surfaceacoustic wave device 1 is an end face reflection type surface waveresonator using a BGS wave as a SH type surface wave. A reflector is notnecessary here because of the end face reflection type. Therefore,miniaturization can be planned.

[0052] In the production of the aforementioned surface acoustic wavedevice 1, the compositions of the materials were variously varied asdescribed above so as to produce surface acoustic wave devices of SampleNos. 1 to 78. Subsequently, the electromechanical coupling coefficientsKBGS (%) of BGS wave, impedance ratios ATT (dB), and change rates ofresonant frequency with respect to temperature (ppm/° C.) were measured.Furthermore, the particle diameter in each of the piezoelectricsubstrates was determined by SEM observation. The results thereof areshown in FIG. 1 and Table 1 to Table 5. Samples outside the scope of theinvention are indicated by an asterisk (*). TABLE 1 particle a m n x y zkBGS ATT diameter fr-TC No. (mol) (mol) (mol) (mol) (mol) (mol) (%) (dB)(μm) (ppm/° C.) 1 1.000 0.167 0.167 0.500 0.470 0.030 29.6 41.6 3.0 42 2* 1.000 0.167 0.167 0.370 0.600 0.030 17.2 28.6 3.5 −27 3 1.000 0.1670.167 0.485 0.465 0.050 34.8 52.3 1.5 51 4 1.000 0.167 0.167 0.488 0.4630.050 40.7 53.3 1.6 −73 5 1.000 0.167 0.167 0.490 0.460 0.050 43.1 58.31.4 −122 6 1.000 0.167 0.167 0.410 0.530 0.060 24.8 49.5 1.7 103 7 1.0000.167 0.167 0.400 0.540 0.060 23.7 47.3 1.5 −32  8* 1.000 0.167 0.1670.390 0.550 0.060 22.1 39.5 1.7 −29 9 1.000 0.156 0.177 0.482 0.4510.067 34.2 41.5 2.9 34 10  1.000 0.155 0.178 0.472 0.450 0.078 48.1 48.22.5 153 11  1.000 0.167 0.167 0.470 0.450 0.080 43.3 42.5 3.8 170 12 1.000 0.156 0.177 0.467 0.449 0.084 53.3 52.0 2.4 184 13  1.000 0.1670.167 0.500 0.410 0.090 49.2 52.4 2.0 −100 14  1.000 0.167 0.167 0.4400.470 0.090 45.9 49.8 2.1 79 15  1.000 0.167 0.167 0.370 0.540 0.09029.5 43.5 2.2 15 16  1.000 0.156 0.178 0.462 0.448 0.090 54.5 54.3 2.198 17  1.000 0.156 0.178 0.463 0.447 0.090 59.3 53.2 2.3 80 18  1.0000.156 0.178 0.462 0.448 0.090 56.7 56.4 2.2 124

[0053] TABLE 2 particle a m n x y z kBGS ATT diameter fr-TC No. (mol)(mol) (mol) (mol) (mol) (mol) (%) (dB) (μm) (ppm/° C.)  19* 1.000 0.1670.167 0.500 0.370 0.130 40.2 43.5 2.1 −301 20 1.000 0.167 0.167 0.4600.410 0.130 55.3 50.8 2.2 −50 21 1.000 0.167 0.167 0.400 0.470 0.13034.2 48.9 2.0 39 22 1.000 0.167 0.167 0.330 0.540 0.130 27.4 44.3 2.0−20 23 1.000 0.156 0.178 0.418 0.442 0.140 43.4 51.2 2.0 −19 24 1.0000.156 0.178 0.380 0.480 0.140 30.0 49.4 2.1 21 25 1.000 0.156 0.1770.386 0.441 0.173 33.0 46.7 2.4 15 26 1.000 0.156 0.178 0.380 0.4400.180 32.3 45.9 2.0 22 27 1.000 0.156 0.178 0.370 0.450 0.180 32.7 50.82.6 51 28 1.000 0.156 0.178 0.390 0.430 0.180 37.1 51.0 2.2 −91 29 1.0000.156 0.178 0.360 0.460 0.180 26.4 45.7 2.1 −12 30 1.000 0.156 0.1780.350 0.450 0.200 27.1 46.5 2.3 −16 31 1.000 0.167 0.167 0.380 0.4100.210 29.2 45.8 1.9 −31 32 1.000 0.167 0.167 0.320 0.470 0.210 25.0 41.92.0 21  33* 1.000 0.156 0.178 0.330 0.450 0.220 23.3 39.4 3.2 −32  34*1.000 0.167 0.167 0.320 0.410 0.270 20.3 36.3 1.8 −30  35* 1.000 0.1670.167 0.440 0.540 0.020 11.7 21.5 3.2 81 36 1.000 0.156 0.177 0.5000.470 0.030 31.6 45.1 2.7 40 37 1.000 0.156 0.177 0.430 0.540 0.030 28.343.8 2.6 28 38 1.000 0.167 0.167 0.470 0.450 0.080 44.3 49.1 2.1 127

[0054] TABLE 3 particle a m n x y z kBGS ATT diameter fr-TC No. (mol)(mol) (mol) (mol) (mol) (mol) (%) (dB) (μm) (ppm/° C.) 39 0.980 0.2920.334 0.488 0.463 0.050 58.1 54.1 1.6 −30 40 1.000 0.292 0.334 0.4880.463 0.050 60.8 56.7 1.6 −53 41 1.020 0.292 0.334 0.488 0.463 0.05059.0 55.3 1.5 −81 42 0.960 0.155 0.178 0.472 0.450 0.078 37.5 46.0 2.2245 43 0.980 0.155 0.178 0.472 0.450 0.078 46.3 48.9 2.7 220 44 1.0000.155 0.178 0.472 0.450 0.078 48.1 48.2 2.5 153 45 0.980 0.156 0.1780.463 0.447 0.090 50.1 51.5 2.1 259 46 1.000 0.156 0.178 0.463 0.4470.090 59.3 53.2 2.3 80 47 1.010 0.156 0.178 0.463 0.447 0.090 54.4 53.32.0 79 48 1.020 0.156 0.178 0.463 0.447 0.090 51.5 51.7 2.3 136 49 0.9300.119 0.119 0.455 0.436 0.109 35.3 45.0 2.4 84 50 0.950 0.119 0.1190.455 0.436 0.109 41.0 46.6 2.0 64 51 0.969 0.119 0.119 0.455 0.4360.109 47.5 49.4 2.5 43 52 1.000 0.119 0.119 0.455 0.436 0.109 49.8 51.22.6 21 53 0.980 0.156 0.178 0.380 0.440 0.180 37.8 51.3 2.2 18 54 1.0000.156 0.178 0.380 0.440 0.180 32.3 45.9 2.0 22 55 0.980 0.156 0.1780.370 0.450 0.180 32.0 49.8 2.3 27 56 1.000 0.156 0.178 0.370 0.4500.180 32.7 50.8 2.6 51 57 0.980 0.156 0.178 0.360 0.460 0.180 26.1 44.42.2 −20 58 1.000 0.156 0.178 0.360 0.460 0.180 26.4 45.7 2.1 −12

[0055] TABLE 4 particle a m n x y z kBGS ATT diameter fr-TC No. (mol)(mol) (mol) (mol) (mol) (mol) (%) (dB) (μm) (ppm/° C.) 59 1.000 0.6560.010 0.490 0.470 0.040 50.9 58.0 2.2 101 60 1.000 0.500 0.166 0.4950.465 0.040 52.7 53.6 2.3 −33 61 1.000 0.333 0.333 0.495 0.465 0.04053.1 58.5 2.3 −40 62 1.000 0.160 0.500 0.495 0.465 0.040 52.0 59.0 2.4−49 63 1.000 0.010 0.656 0.490 0.470 0.040 49.7 55.9 2.2 42 64 1.0000.167 0.167 0.490 0.460 0.050 43.1 58.3 1.4 −122 65 1.000 0.292 0.3340.490 0.460 0.050 63.5 59.3 1.5 −97 66 1.000 0.333 0.333 0.490 0.4600.050 63.9 59.0 1.7 −60 67 1.000 0.167 0.167 0.488 0.463 0.050 40.7 53.31.6 −73 68 1.000 0.230 0.230 0.488 0.463 0.050 51.5 54.1 1.8 −61 691.000 0.292 0.334 0.488 0.463 0.050 60.8 56.7 1.6 −53 70 1.000 0.3330.333 0.488 0.463 0.050 61.2 57.4 1.4 40 71 1.000 0.167 0.167 0.4850.465 0.050 34.8 52.3 1.5 51 72 1.000 0.292 0.334 0.485 0.465 0.050 54.254.7 1.5 96 73 1.000 0.333 0.333 0.485 0.465 0.050 56.1 55.8 1.8 104 741.000 0.119 0.119 0.470 0.450 0.080 48.5 48.1 2.2 38 75 1.000 0.1390.139 0.470 0.450 0.080 52.8 55.2 2.3 65  76* 1.000 0.167 0.167 0.4700.450 0.080 38.2 38.4 3.8 170

[0056] TABLE 5 particle a m n x y z Sr kBGS ATT diameter fr-TC No. (mol)(mol) (mol) (mol) (mol) (mol) (mol) (%) (dB) (μm) (ppm/° C.) 77 0.9500.015 0.017 0.458 0.493 0.050 0.050 51.2 58.2 1.8 −21 78 0.950 0.0150.024 0.465 0.485 0.050 0.050 44.2 55.3 2.3 36

[0057] Sample Nos. 1 to 38 in Tables 1 and 2 are examples in which x, y,and z are varied while a=1 and m+n=⅓ in the aforementioned formula. FIG.1 shows changes of the electromechanical coupling coefficient withchanges of y and z in the aforementioned cases.

[0058] As is clear from FIG. 1, the electromechanical couplingcoefficients vary with changes of z, and reach maximum values in theneighborhood of z=0.1. It is clear that the impedance ratios (ATT) aresufficiently large, 40 dB or more, in the range of 0.03≦z≦0.21. On theother hand, in Sample Nos. 33, 34, and 35, which are out of the range of0.03≦z≦0.21, sinterability is degraded and the impedance ratios arereduced.

[0059] When y>0.54, the impedance ratios are reduced, and when y<0.41,the impedance ratios and the electromechanical coupling coefficients arelarge, although heat resistance is degraded.

[0060] Since x satisfies x+y+z=1, if y or z becomes out of theaforementioned preferable range as a result of selection of x,characteristics are degraded.

[0061] As is confirmed from the results shown in Tables 1 and 2, theimpedance ratios are excellent when x falls within the range of0.32≦x≦0.50.

[0062] In Sample Nos. 39 to 58 as shown in Table 3, the value of a isvaried in the range of 0.93 to 1.02, while x, y and z fall within theaforementioned preferable ranges. As is clear from Table 3, theimpedance ratios and the electromechanical coupling coefficients are notdegraded by a large degree in spite of changes of a. Therefore, it isclear that excellent piezoelectric characteristics can be exhibited whena falls within the range of 0.93≦a≦1.02. When a is out of this range,sinterability is degraded.

[0063] Table 4 shows examples of Sample Nos. 59 to 76 in which m and nare varied while x, y, and z fall within the preferable rangesdetermined from Tables 1 and 2. It is usually believed that theperovskite structure is stable when m+n=⅓.

[0064] However, it is clear from the results of Sample Nos. 59 to 76that the impedance ratios become 40 or more when m +n falls within therange of 0.24≦m+n≦0.67, and the impedance ratios are not degradedcompared to that in the case where m+n =⅓. In particular, it is clearthat when m and n fall within the ranges of 0.46≦m+n≦0.67, 0.01≦m≦0.66and 0.01≦n≦0.66, the electromechanical coupling coefficients KBGSpreferably become very large, e.g., 50.9% or more.

[0065] Table 5 shows Sample Nos. 77 and 78 in which Sr was substitutedfor part of the Pb in the A site. It is clear that high impedance ratiosand electromechanical coupling coefficients kBGS can also be achieved incompositions in which Sr is present at the A site.

[0066] The impedance ratios are reduced for Sample Nos. 3, 13, and 76 inwhich particle diameters of the sintered materials exceed about 3 μm.Therefore, the particle diameter of the sintered material is preferablyabout 3 μm or less. Regarding defects and pores in the sinteredmaterial, effects similar to those in the above description areexhibited, so that, as is assumed from the actions due to the changes ofthe particle diameter of the sintered material, the defects and poresare also preferably about 3 μm or less.

[0067] With the Samples which are within the scope of the presentinvention, excellent impedance ratios can be achieved and a wide rangeof electromechanical coupling coefficients kBGS of about 30% to about50% can be achieved.

[0068] In the aforementioned examples, the case where the presentinvention has been applied to the end face reflection type surface wavedevice using a SH type surface wave has been explained, although thepiezoelectric ceramic composition for a surface acoustic wave deviceaccording to the present invention can be used for surface acoustic wavedevices using surface waves, such as a Rayleigh wave, other than SHtype.

What is claimed is:
 1. A piezoelectric ceramic composition for a surfaceacoustic wave device represented by the formulaA_(a)Zr_(x)Ti_(y)(Ni_(m)Mn_(n)Nb_(2/3))_(z)O₃, wherein: x+y+z=1;0.93≦a≦1.02; 0.32≦x≦0.50; 0.41≦y≦0.54; 0.03≦z≦0.21; 0.24≦m+n≦0.67; andwherein A is Pb or the combination of Pb and at least one member of thegroup consisting of Ba, Ca and Sr.
 2. A piezoelectric ceramiccomposition for a surface acoustic wave device according to claim 1,wherein 0.46≦m+n≦0.67; 0.01≦m≦0.66; and 0.01≦n≦0.66.
 3. A piezo electricceramic composition for a surface acoustic wave device according toclaim 2, wherein A is Pb.
 4. A piezoelectric ceramic composition for asurface acoustic wave device according to claim 2, wherein A is acombination of Pb and at least one member selected from the groupconsisting of Ba, Ca, and Sr.
 5. A piezoelectric ceramic composition fora surface acoustic wave device according to claim 4, wherein said memberof the group is Sr.
 6. A piezoelectric ceramic composition for a surfaceacoustic wave device according to claim 1, wherein A is Pb.
 7. Apiezoelectric ceramic composition for a surface acoustic wave deviceaccording to claim 1, wherein A is a combination of Pb and at least onemember selected from the group consisting of Ba, Ca, and Sr.
 8. Apiezoelectric ceramic composition for a surface acoustic wave deviceaccording to claim 7, wherein said member of the group is Sr.
 9. Apiezoelectric ceramic comprising a sintered piezoelectric ceramiccomposition for a surface acoustic wave device according to claim
 1. 10.A piezoelectric ceramic according to claim 9, having a grain diameter ofabout 3 μm or less.
 11. A piezoelectric ceramic according to claim 10,wherein the size of pores and defects in the piezoelectric ceramic areabout 3 μm or less.
 12. A piezoelectric ceramic according to claim 11,wherein the absolute value of the change rate of resonant frequency withrespect to temperature is about 100 ppm/° C. or less.
 13. Apiezoelectric ceramic comprising a sintered piezoelectric ceramiccomposition for a surface acoustic wave device according to claim
 2. 14.A piezoelectric ceramic according to claim 13, having a grain diameterof about 3 μm or less.
 15. A surface acoustic wave device comprising apiezoelectric substrate comprising the piezoelectric ceramic, accordingto claim 13; and an interdigital transducer on the piezoelectricsubstrate.
 16. A surface acoustic wave device according to claim 15,wherein the interdigital transducer is configured to generate a SH typesurface acoustic wave on the piezoelectric substrate.
 17. A surfaceacoustic wave device according to claim 16, wherein the piezoelectricsubstrate has a pair of edges defining a surface on which theinterdigital transducer is disposed, and outermost electrode fingers ofthe interdigital transducer are flush with said edges.
 18. A surfaceacoustic wave device comprising a piezoelectric substrate comprising thepiezoelectric ceramic according to claim 9; and an interdigitaltransducer on the piezoelectric substrate.
 19. A surface acoustic wavedevice according to claim 18, wherein the interdigital transducer isconfigured to generate a SH type surface acoustic wave on thepiezoelectric substrate.
 20. A surface acoustic waive device accordingto claim 19, wherein the piezoelectric substrate has a pair of edgesdefining a surface on which the interdigital transducer is disposed, andoutermost electrode fingers of the interdigital transducer are flushwith said edges.